The present invention relates to a liquid crystal display device and a manufacturing method of the same, and it particularly relates to a ferroelectric liquid crystal display device having a large screen and being capable of high-definition display, as well as relates to a manufacturing method of the same.
Ferroelectric liquid crystal has excellent properties such as excellent memory effect, high-speed response, and a wide visual angle, and in the case where it is applied to a display device of a simple matrix type, the display device becomes capable of high-definition large-capacity display (see N. A. Clark and S. T. Lagerwall, Appl. Phys. Lett., 36 (1980), pp. 899 (Date of Publication: Jun. 1, 1980)). An example of a conventional structure of a ferroelectric liquid crystal display device is shown in FIG. 13 which is a cross-sectional view of the same.
The ferroelectric liquid crystal display device is provided with two glass substrates 112a and 112b. On the glass substrate 112a, a plurality of transparent signal electrodes 113a made of indium tin oxide (ITO) or the like are formed so as to be parallel with each other, on which a transparent insulating film 114a made of SiO2 (silicon dioxide) or the like is formed.
On the glass substrate 112b facing the glass substrate 112a, transparent scanning electrodes 113b made of ITO or the like are formed so as to be parallel with each other in a direction crossing the direction of the signal electrodes 113 at a right angle, and the scanning electrodes 113b are also covered with a transparent insulating film 114b made of SiO2.
On the transparent insulating films 114a and 114b, alignment films 115a and 115b having been subjected to a uniaxial alignment processing such as a rubbing operation are formed, respectively. As the alignment films 115a and 115b, an organic polymer film such as a polyimide film, a nylon film, or a polyvinyl alcohol film, a SiO (silicon monoxide) rhombic vapor deposition film, or the like is used. In the case where an organic polymer film is adapted so as to be used as the alignment films 115a and 115b, such alignment processing as to align the liquid crystal molecules so as to be substantially parallel with respect to the electrode substrates is applied to the alignment films 115a and 115b. 
The glass substrate 112a on which the signal electrodes 113a, the transparent insulating film 114a, and the alignment film 115a are laminated in this order is hereinafter referred to as an electrode substrate 110. Likewise, the glass substrate 112b on which the scanning electrodes 113b, the transparent insulating film 114b, and the alignment film 115b are laminated in this order is hereinafter referred to as an electrode substrate 111.
The electrode substrates 110 and 111 are combined to each other with a sealing material 116 which is applied thereto except a part serving as an injection opening, through which subsequently ferroelectric liquid crystal 117 is injected into a space formed between the alignment films 115a and 115b. Then, the injection opening is sealed with the sealing material 130.
The electrode substrates 110 and 111 thus assembled are sandwitched between polarization plates 118a and 118b which are arranged so that polarization axes thereof cross each other at a right angle. In the case where a display area is large, spherical spacers 119 are dispersely provided between the electrode substrates 110 and 111 so that the electrode substrates 110 and 111 are parallel with each other, resulting in that a uniform cell thickness is achieved.
The ferroelectric liquid crystal molecules 120 have spontaneous polarization 121 in a direction orthogonal to a direction of a major axis of the molecule 120, as shown in FIG. 14. Therefore, each of the ferroelectric liquid crystal molecules 120 moves along a surface of a conical locus 122 in response to a force proportional to a vector product of the spontaneous polarization 121 and an electric field which is generated by a voltage applied across the signal electrode 113a and the scanning electrode 113b. 
Therefore, to the eyes of an observer, the ferroelectric liquid crystal molecule 120 appears to switch between generator positions A and B in the conical locus 122, as shown in FIG. 15. Here, in the case where, for example, the polarization plates 118a and 118b are arranged so that a direction of the polarization axis of one of the polarization plates 118a and 118b agrees with the molecular major axis direction 138a of the molecule 120 at the position A and that a direction of the polarization axis of the other polarization plate agrees with a direction 138b, a dark field is obtained when the molecules 120 switch to the position A. A bright field is obtained due to birefringence when the molecules 120 switch to the position B.
Furthermore, respective alignment states of the ferroelectric liquid crystal molecules 120 in the positions A and B are equivalent in elastic energy. Accordingly, after the electric field by the voltage across the signal electrodes 113a and the scanning Helectrode 113b disappears, the alignment state, or the optical state, of the molecule 120 is maintained. This is a so-called memory effect of ferroelectric liquid crystal. The memory effect is a characteristic that the conventional nematic liquid crystal does not possess, and in combination with the high-speed response due to the spontaneous polarization, enables a display device using the ferroelectric liquid crystal to realize high-definition large-capacity display in a simple matrix arrangement.
On the other hand, the Japanese Publication for Laid-Open Patent Application No. 311213/1997 (Tokukaihei 9-311213, Date of Publication: Dec. 2, 1997) discloses the following manufacturing method: a micell colloid aqueous solution mainly consisting of transparent conductive particles, pigment particles, a surfactant, and a supporting electrolyte, in which the transparent conductive particles and the pigment particles are surrounded by the surfactant, is prepared by the wet electrolytic method, and the micell is broken by electrolysis so that the conductive particles and the pigment particles are separated and deposited on electrodes.
To realize moving picture display by means of a display device with a large screen, it is necessary to lower wire resistances of signal electrodes and scanning electrodes so as to reduce deformation of waveforms of applied voltages. In other words, for high-speed driving of a display device with a large screen, it is necessary to lower wire resistances so that waveforms of voltages applied to each pixel do not deform. A wire resistance required is determined by a capacitance of the display device and a pulse width of a driving waveform. More specifically, it is necessary to set the wire resistance low so as to fall in a predetermined range as shown in the Patent Application No. 361209/1997 (Tokuganhei 9-361209, corresponding to U.S. patent application Ser. No. 09/217,162) which the Applicant of the present invention has filed.
Therefore, metal wires are used as supplementary wires, but such an arrangement undergoes, apart from problems related to fine processing and adhesion to substrates, such problems as line defects, etch selectivity of metal or transparent electrodes (transparent conductive films), and flatness of a substrate.
Furthermore, there exist in transparent electrodes many projections which are caused by nodules of a target used in film formation and in turn cause disorder of alignment and vertical leakage (leakage between upper and lower transparent electrodes). The following description will explain these problems.
[Line Defects]
In the process of forming wires in a liquid crystal display device, dusts, defects in formed resist patterns, metal wiring defects, defects in formed transparent electrodes, etc. cause defects in wires. Such defects lead to display defects such as line defects and pixel defects after completion of a panel.
[Etching Selectivity of Metal or Transparent Electrodes]
The large display device manufacturing process includes, relating to the wiring for forming signal electrodes and scanning electrodes, a metal wire forming step and a transparent electrode forming step, through which metal wires and transparent electrodes are formed so as to be electrically connected. Here, sometimes acidic etching liquid used in a transparent electrode patterning step permeates to the metal wiring side, and for requirements of some designs or for other reasons, the metal wires are exposed to the etching liquid used for forming the transparent electrodes. To avoid corrosion of metal in the foregoing steps, it is necessary to select a metal material with resistance against the transparent electrode etching liquid.
[Flatness of Substrate]
The large display device manufacturing process includes the foregoing metal wire forming step and transparent electrode forming step, and further, relating to formation of color filters and the like, a step of forming resin which contains pigments. Since a surface of the substrate processed through the foregoing steps have raised and recessed portions caused through the foregoing steps, it is difficult to achieve flatness of the substrate. In the case of a liquid crystal display device, such roughness of the substrate surfaces leads to such problems as irregular liquid crystal alignment, irregular discharge, non-uniformity in distance between substrates, and non-uniformity in display. Therefore, it is necessary to decrease the steps which tend to make surfaces of the substrates rough, as well as to add steps for ensuring flatness of the substrates.
[Alignment Disorder and Vertical Leakage due to Projections on Transparent Electrodes]
In formation of the transparent electrodes by the sputtering method or the vapor deposition method, nodules 142 are formed on a target 141, as shown in FIG. 16(a). The nodules 142 grow in size after formation as the sputtering operation goes on, and past the elastic limit, they are broken into pieces as shown in FIG. 16(b), which become nuclei of new nodules 142. Upon the breakdown of the nodules 142, many segments 144 of the transparent electrode material adhere to an opposite substrate 143. In the case where a cell gap between the substrates 144 and 143 is small, such conductive segments 144 or projections tend to cause alignment disorder or vertical leakage upon application of an electric field, as shown in FIG. 16(c).
[Reduction of Photoprocess Steps]
A process for manufacturing a liquid crystal display using metal wires as supplementary wires generally requires three steps of photoprocessing. More specifically, a step of patterning a light blocking layer to form a black matrix, a transparent electrode patterning step, and a metal wire patterning step require photoprocessing, which means that photoprocessing has to be carried out three times with respect to one substrate. Since the other opposite substrate requires similar patterning steps, photoprocessing is required to be carried out six times in total. Furthermore, photoprocessing is also carried out to form spacers for control of the cell gap, resulting in that photoprocessing has to be carried out seven times in total.
The present invention was made in light of the aforementioned problems, and the object of the present invention is to provide a liquid crystal display device with a large display screen which has low resistance wiring and excels in flatness of substrates, and a method for manufacturing the same at a good yield.
To achieve the foregoing object, a liquid crystal display device of the present invention, which is a liquid crystal display device provided with a substrate on which scanning electrodes are laid and a substrate on which signal electrodes are laid, is arranged so that a metal material, a transparent electrode material, and a conductive resin are used for forming either the scanning electrodes or the signal electrodes, or both of the same.
With the foregoing arrangement, it is possible to lower resistance of the electrodes without impairing flatness of the substrate, and therefore, it is possible to provide a large-scale liquid crystal display device which does not undergo alignment disorder caused by roughness of the substrate, incomplete switching behaviors of liquid crystal due to the lowering of voltages, the lowering of contrast, defects in gray scale, etc. Furthermore, it undergoes neither display defects nor vertical leakage, and accordingly excels in display performance.
Furthermore, to achieve the foregoing object, a liquid crystal display device of the present invention, which is a liquid crystal display device provided with a substrate on which scanning electrodes are laid and a substrate on which signal electrodes are laid, is arranged so that a metal material, a transparent electrode material, and a conductive color filter are used for forming either the scanning electrodes or the signal electrodes, or both of the same.
With the foregoing arrangement, it is possible to lower resistance of the electrodes without impairing flatness of the substrate, and therefore, it is possible to provide a large-scale liquid crystal display device which does not undergo alignment disorder caused by roughness of the substrate, incomplete switching behaviors of liquid crystal due to the lowering of voltages, the lowering of contrast, defects in gray scale, etc. Furthermore, it undergoes neither display defects nor vertical leakage, and accordingly excels in display performance. Moreover, since the conductive color filter is used, an electrode structure serving as a color filter as well can be realized.
Furthermore, to achieve the foregoing object, a liquid crystal display device of the present invention, which includes a substrate on which scanning electrodes are laid, and a substrate on which signal electrodes are laid, is arranged so that (1) each of either the scanning electrodes or the signal electrodes, or both of the same, has an electrode structure composed of at least a transparent electrode and a conductive resin layer which are laminated in this order, and (2) an insulating layer serving as a light blocking layer and a spacer is provided on at least one of the substrates.
Furthermore, to achieve the foregoing object, a liquid crystal display device of the present invention, which includes a substrate on which scanning electrodes are laid, and a substrate on which signal electrodes are laid, is arranged so that (1) each of either the scanning electrodes or the signal electrodes, or both of the same, has an electrode structure composed of at least a transparent electrode and a conductive color filter layer which are laminated in this order, and (2) an insulating layer serving as a light blocking layer and a spacer is provided on at least one of the substrates.
According to any one of the foregoing arrangements, the insulating layer serves as a light blocking layer for preventing light exchange between the pixels, as well as serves as spacers for keeping the substrates at a uniform distance. Therefore, as compared with a case where the light blocking layer and the spaces are formed independently, photoprocessing operations are reduced in number, thereby resulting in the lowering of costs.
To achieve the foregoing object, a method for manufacturing a liquid crystal display device of the present invention includes the step of subjecting a surface of either the conductive resin layer or the conductive color filter layer to either pressing or polishing, or both of the same, so as to improve flatness of the surface.
By the foregoing method, the flatness of the substrate surface is further enhanced by pressing or polishing.
To achieve the foregoing object, a method for manufacturing a liquid crystal display device of the present invention includes the step of forming the conductive resin layer, the conductive color filter layer, or the second conductive resin layer by the micell electrolytic method.
By the foregoing method, conductive particles, or conductive particles plus pigment particles, are deposited on electrodes by the micell electrolytic method, resulting in that a desired conductive layer can be formed.